Small-sized variable magnification optical system

Abstract

A variable magnification optical system comprises at least three optical units which are a first moving optical unit, a fixed optical unit and a second moving optical unit. The three optical units are arranged in that order in a propagation direction of light, and a variation of magnification is effected by a relative movement between the first moving optical unit and the second moving optical unit. If a ray which exits from an object and enters the variable magnification optical system, and passes through a center of a stop of the variable magnification optical system and reaches a center of a final image plane is represented as a reference axis ray, the second moving optical unit has a cross-sectional shape which is asymmetrical in a plane which contains the reference axis, and a curved reflecting surface which is inclined with respect to the reference axis, and the direction of the entering reference axis and the direction of the exiting reference axis of the second moving optical unit are parallel to each other and differ from each other by 180°, the variable magnification optical system being arranged in such a manner that a final image is formed after an intermediate image is formed at least twice.

We claim: 
     
       1. A variable magnification optical system comprising at least three optical units, said at least three optical units being a first moving optical unit, a fixed optical unit and a second moving optical unit which are arranged in that order in a propagation direction of light, a variation of magnification being effected by a relative movement between said first moving optical unit and said second moving optical unit, wherein if a ray which exits from an object and enters said variable magnification optical system, and passes through a center of a stop of said variable magnification optical system and reaches a center of a final image plane is represented as a reference axis ray; a reference axis ray which is incident on any surface of said variable magnification optical system or enters any of said optical units is represented as an entering reference axis of said any surface or said any optical unit; a reference axis ray which exits from said any surface or said any optical unit is represented as an exiting reference axis of said any surface or said any optical unit; a point at which the entering reference axis intersects with said any surface is represented as a reference point; a direction in which the reference axis ray travels from an object side toward an image plane along the entering reference axis is represented as a direction of the entering reference axis; and a direction in which the reference axis ray travels from the object side toward the image plane along the exiting reference axis is represented as a direction of the exiting reference axis,   said second moving optical unit has a cross-sectional shape which is asymmetrical in a plane which contains the reference axis, and a curved reflecting surface which is inclined with respect to the reference axis, and the direction of the entering reference axis and the direction of the exiting reference axis of said second moving optical unit are parallel to each other and differ from each other by 180°, said variable magnification optical system being arranged in such a manner that a final image is formed after an intermediate image is formed at least twice.   
     
     
       2. A variable magnification optical system according to claim 1, wherein said fixed optical unit is an optical unit having the largest ratio of (a lateral magnification at a wide-angle end) to (a lateral magnification at a telephoto end) of all the optical units. 
     
     
       3. A variable magnification optical system according to claim 1, wherein said first moving optical unit moves toward said fixed optical unit during a variation of magnification from a wide-angle end toward a telephoto end. 
     
     
       4. A variable magnification optical system according to claim 1, wherein said second moving optical unit includes an optical element which is formed as one transparent body on which two refracting surfaces and a plurality of internal curved reflecting surfaces are formed. 
     
     
       5. A variable magnification optical system according to claim 1, wherein said first moving optical unit includes an optical element which is formed as one transparent body on which two refracting surfaces and a plurality of internal curved reflecting surfaces inclined with respect to the reference axis are formed, the direction of the entering reference axis and the direction of the exiting reference axis of said optical element being parallel to and the same as each other. 
     
     
       6. A variable magnification optical system according to claim 1, wherein said first moving optical unit includes an optical element which is formed as one transparent body on which two refracting surfaces and a plurality of internal curved reflecting surfaces inclined with respect to the reference axis are formed, the direction of the entering reference axis and the direction of the exiting reference axis of said optical element being parallel to each other and different from each other by 180°. 
     
     
       7. A variable magnification optical system according to claim 5, wherein said first moving optical unit forms an intermediate image in its inside. 
     
     
       8. A variable magnification optical system according to claim 1, wherein said fixed optical unit includes an optical element which is formed as one transparent body on which two refracting surfaces and a plurality of internal curved reflecting surfaces inclined with respect to the reference axis are formed, the direction of the entering reference axis and the direction of the exiting reference axis of said optical element being parallel to and the same as each other. 
     
     
       9. A variable magnification optical system according to claim 1, wherein said fixed optical unit includes an optical element which is formed as one transparent body on which two refracting surfaces and a plurality of internal curved reflecting surfaces inclined with respect to the reference axis are formed, the direction of the entering reference axis and the direction of the exiting reference axis of said optical element being parallel to each other and different from each other by 180°. 
     
     
       10. A variable magnification optical system according to claim 1, wherein said fixed optical unit includes an optical element which is formed as one transparent body on which two refracting surfaces and a plurality of internal curved reflecting surfaces inclined with respect to the reference axis are formed, the exiting reference axis of said optical element being inclined with respect to the entering reference axis thereof. 
     
     
       11. A variable magnification optical system according to claim 1, wherein said stop is located on the object side of said first moving optical unit, said stop being fixed during the variation of magnification. 
     
     
       12. A variable magnification optical system comprising at least three optical units, said at least three optical units being a first moving optical unit, a fixed optical unit, and a second moving optical unit which are arranged in that order in a propagation direction of light, a variation of magnification being effected by a relative movement between said first moving optical unit and said second moving optical unit, wherein if a ray which exits from an object and enters said variable magnification optical system, and passes through a center of a stop of said variable magnification optical system and reaches a center of a final image plane is represented as a reference axis ray; a reference axis ray which is incident on any surface of said variable magnification optical system or enters any of said optical units is represented as an entering reference axis of said any surface or said any optical unit; a reference axis ray which exits from said any surface or said any optical unit is represented as an exiting reference axis of said any surface or said any optical unit; a point at which the entering reference axis intersects with said any surface is represented as a reference point; a direction in which the reference axis ray travels from an object side toward an image plane along the entering reference axis is represented as a direction of the entering reference axis; and a direction in which the reference axis ray travels from the object side toward the image plane along the exiting reference axis is represented as a direction of the exiting reference axis,   each of said first moving optical unit, said fixed optical unit, and said second moving optical unit includes an optical element which is formed as one transparent body on which two refracting surfaces and at least one internal curved reflecting surface inclined with respect to the reference axis are formed,   said second moving optical unit having a cross-sectional shape which is asymmetrical in a plane which contains the reference axis, and the direction of the entering reference axis and the direction of the exiting reference axis of said second moving optical unit are parallel to each other and differ from each other by 180°, said variable magnification optical system being arranged in such a manner that a final image is formed after an intermediate image is formed at least twice.   
     
     
       13. A variable magnification optical system according to claim 12, wherein, during a variation of magnification from a wide-angle end toward a telephoto end, an optical path length between said first moving optical unit and said fixed optical unit becomes shorter, whereas an optical path length between said fixed optical unit and said second moving optical unit becomes longer. 
     
     
       14. A variable magnification optical system according to claim 12, wherein, during the variation of magnification, an optical path length which extends from the object to the final image forming plane is varied with the final image forming plane spatially fixed. 
     
     
       15. A variable magnification optical system according to claim 12, wherein said stop is located on the object side of said first moving optical unit, said stop being fixed during the variation of magnification. 
     
     
       16. An image pickup apparatus comprising said variable magnification optical system according to claim 1, said image pickup apparatus being arranged to form an image of an object to be photographed, on an image pickup surface of an image pickup medium.